Advertisements or other messages shown on the Internet, commonly but not exclusively “banner ads”, are typically created by an advertiser and provided to an advertiser server (“ad server”) as a whole unit. The advertiser server is typically a physically and commercially separate entity which cooperates with another typically distinct party, an on-line publisher or web-site operator, such as a search engine, newspaper, or web log (“blog”) to place advertisements in the web-site operated by the distinct party, to be displayed to a viewer. In such systems, the advertiser creating and providing the advertisement does not have the ability to easily alter the advertisement once provided to the advertiser server, or to dynamically alter the advertisement, or to obtain feedback based on a large number of different advertisements.